The structure of the transposable DNA called the F element has been studied in Drosophila melanogaster. Three DNA regions containing F elements were isolated from one stock of D. melanogaster and the boundaries of the F element were sequenced. The corresponding regions were isolated and partially sequenced from a different stock of D. melanogaster; the F element was absent from these regions. The comparison of the filled and empty sites showed that F element insertion is accompanied by target site duplications of variable length. A female sterile mutation that leads to homeotic transformations in Drosophila is being studied. We propose to isolate the gene by DNA cloning. To this end we have obtained DNA probes from the chromosomal region where the gene resides and have initiated a "chromosomal walk". To achieve transformation in Drosophila we have constructed plasmids in which the alcohol dehydrogenase gene has been inserted within transposable elements. These plasmids will be injected into Drosophila embryos by our collaborators in Switzerland.